Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 13 Apr 2017 17:16:20 +0200 | Subject | Re: [PATCH v2] sched/fair: update scale invariance of PELT |
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On 13 April 2017 at 15:39, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, Apr 11, 2017 at 09:52:21AM +0200, Vincent Guittot wrote: > >> > Secondly, what's up with the util_sum < LOAD_AVG_MAX * 1000 thing? >> >> The lost idle time makes sense only if the task can also be "idle" >> when running at max capacity. When util_sum reaches the >> LOAD_AVG_MAX*SCHED_CAPACITY_SCALE value, all tasks are considered to >> be the same as we can't make any difference between a task running >> 400ms or a task running 400sec. It means that these tasks are "always >> running" tasks even at max capacity. In this case, there is no lost >> idle time as they always run and tracking and adding back the lost >> idle time because we run at lower capacity doesn't make sense anymore >> so we discard it. > > Right, this is the point we reached yesterday with the too low F. At > that point you cannot know and we assuming u=1, F<1 -> u=1, F=1, which > is a sensible assumption. > >> Then an always running task can have a util_sum that is less than the >> max value because of the rounding (util_avg varies between >> [1006..1023]), so I use LOAD_AVG_MAX*1000 instead of LOAD_AVG_MAX*1024 > > OK, so the reason util_avg varies is because we compute it wrong. And I > think we can easily fix that once we pull out all the factors (which > would mean your patch and the pulling out of weight patch which still > needs to be finished).
That would be great to remove this unwanted variation.
> > But you're comparing against util_sum here, that behaves slightly > different. I think you want 'util_sum >= 1024 * (LOAD_AVG_MAX - 1024)' > instead.
yes, the variation happens on the util_sum
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